Matriculation Chemistry Reaction Kinetics part 1.pdf

8/12/2019 Matriculation Chemistry Reaction Kinetics part 1.pdf

1/13

Objectives:

1. Define reaction rate, average rate,

instantaneous rate and initial rate.2. Determine the reaction rate based on a

differential equation.

11.0 REACT!" #"ETC$


2/13

Chemical kinetics is the stud% of the rates of

chemical reactions, the factors that affect theserates, and the reaction mechanisms b% &hich

reactions occur.

'Time'!(timum %ield'!(timum conditions

control over reaction,

obtain (roducts economicall%,

using o(timum conditions

m(ortant

industrial (rocess

REACT!" #"ETC$


3/13

rate )d*+

dt d*+ ) change in concentration of +

+ecause *A decreases &ith time, d*A is negative.

rate ) d*A ) change in concentration of A

E-am(le A B

Rate of reaction

/Reaction rateis the change in the concentrationof a reactant or a (roduct &ith time.

/nit of rate mol '1 s'13/rate

dt ) (eriod of time

Time

1

d*A

dt'


4/13

A +

time

rate ) ' d*A

dt

rate )d*+

dt *A 4

*+ 5


5/13

/ The average rateis the rate over a (eriod of time.

/ The rate of reaction at a given time is called an

instantaneous rate of reaction./ The instantaneous rate at the beginning of a

reaction is called theinitial rate of reaction.

/ nstantaneous rate is determined from a gra(h of

concentration vs time b% dra&ing a line tangent tothe curve at that (articular time.

Rate of reaction


6/13

Reaction6

72!2(aq)72!(l)8 9 !2(g)

Reaction rates are obtained

from the slo(es of the straight

lines

An average ratefrom the

(ur(leline.

The instantaneous rateatt ):00 s from the redline.

The initial ratefrom the blue

line.

Rate of reaction

blue red

(ur(le


7/13

instantaneous rate= rate at a specific time

+r2aq38 7C!!7 aq3 2+r'aq38 278aq38 C!2g3

average rate) 'd*Br2

dt) '

*+r2final ; *+r2initial

tfinal ' tinitial


8/13

The differential rate equation

Rate )dt

d[D]d1

dtd[C]

c1

dt]d[B

b1

dtd[A]

a1

===

Consider the reaction, aA 8 b+ cC 8 dD

A differential rate equation enables the relationshi(bet&een the rate of disa((earance of reactants and

the formation of (roducts.

a,b,c and d are the stoichiometric coefficients


9/13

E-am(le6

The formation of "7:,

The differential rate equation

"2g3 8 :72g3 2"7:g3

The differential rate equation is

dt

]d[NH

2

1

dt

]d[H

3

1

dt

]d[N 322==Rate )

The equation means that the rate of disa((earance

of "2is 1


10/13

Consider the reaction, 27 728 2,

determine the rate of disa((earance of 7 &hen

the rate of 2formation is 1.= - 10'> ? s'1.

dt]d[I

dt]d[H

dtd[HI]

21 22 ==

Example 1:

Rate )

Rate )dt

]d[I

dt

d[HI]

2

1 2=

dt

]d[I2 ) 1.= 10'>

Solution:

dt

d[HI]) 2 1.= 10'> ) !" 1#$"% s$1


11/13

E&ERC'SE 1:

7%drogen gas (roduced non(olluting (roduct is

&ater va(our &hen react in !2 due to this reaction

has been used for fuel aboard the s(ace shuttle,

and ma% be used b% Earth'bound engines in the

near future. 272g3 8 !2g3 272!g3

/ E-(ress the rate in terms of changes in *72,

*!2 and *72! &ith time.

/ @hen *!2 is decreasing at 0.2: mol '1s'1, at

&hat rate is *72! increasing

(0.46 mol L-1

s-1

)


12/13

Consider the reaction,

"!g3 8 !2g3 2"!2g3.

$u((ose that at a (articular time during the

reaction nitric o-ide "!3 is reacting at the rate of

0.0>> ? s'1

a3 At &hat rate is "!2being formed

b3 At &hat rate is molecular o-%gen reacting

Exercise (:


13/13

Consider the reaction,

"2g3 8 :7

2g3 2"7

:g3

$u((ose that at a (articular moment during the

reaction molecular h%drogen is reacting at the rate

of 0.0B ? s'1

a3 At &hat rate is ammonia being formed

b3 At &hat rate is molecular nitrogen reacting

Exercise :

Matriculation Chemistry Reaction Kinetics part 1.pdf

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